1. Field of the Invention
The present invention relates to a hydraulic control system of an automatic transmission for a vehicle and, more particularly, to the hydraulic control system which can improve shift feeling and fuel consumption ratio by permitting a 5-speed change to be realized and a line pressure to be variably controlled.
2. Description of Related Art
Generally, a conventional automatic transmission for a vehicle includes a torque converter, a multi-stage shift gear mechanism connected to the torque converter, and a plurality of friction elements, which are actuated by hydraulic pressure, for selecting one of the gear stages of the shift gear mechanism.
The hydraulic pressure pressurized by an oil pump is supplied to the friction elements and a plurality of control valves.
The torque converter includes a pump impeller connected to an output shaft of an engine to rotate therewith, a turbine runner connected to an input shaft of the transmission to operate therewith, and a stator located between the pump impeller and the turbine runner.
Automatic speed change is realized by a planetary gear unit operated by the friction elements such as clutches or a kick-down band brake.
The friction elements are selectively actuated by the valves of the hydraulic control system which change the direction of the hydraulic pressure. A manual valve is designed to receive the hydraulic pressure from the oil pump through a port, which is closed or opened in accordance with position of a shift lever, and connected to a shift control valve by a passage to supply the hydraulic pressure thereto.
Such an automatic transmission for vehicle is disclosed in U.S Pat. No. 5,003,842.